What is purva-paksa?

"Purva-paksa: The opposing point of view." That's the glossary definition provided by Edwin F. Bryant in his book, The Yoga Sutras of Patañjali: A New Edition, Translation, and Commentary. Yogacharya B.K.S. Iyengar describes the process of paksa pratipaksa: "Paksa means to take one side (in an argument), to espouse one view: while pratipaksa conveys the idea of taking the opposite position." (From Light on the Yoga Sutras of Patañjali, B.K.S. Iyengar.) Iyengar advises studying "opposite forces with calmness and patience."